Export to PDF - missing text

something strange is happening. I'm new to Gimp (ver 2.8.8, on Linux Mint)

I just created a simple poster (8.5 by 11 inches) and imported one small jpeg, and I added some text (each in their own layers). It looks nice in Gimp, but when I export as PDF, it's missing some of the text. I had to keep making the font size smaller before it eventually printed to the PDF. Anyone know why it looks nice it Gimp, but missing some text in PDF export?